• 대한화학회지
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• 제46권1호
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• pp.69-75
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• 2002

조합화학 기법을 이용하여 청색 및 적색 발광을 하는 $Y_{1-x}(P_{1-y-z}Nb_yV_z)O_4:Eu_x$ 형광체를 합성하였다. 합성한 $Y_{1-x}(P_{1-y-z}Nb_yV_z)O_4:Eu_x$ 형광체에 대하여 254 nm 및 147 nm 여기 하에서의 발광 세기에 관한 라이브러리를 완성하였고, 또한 형광체의 결정성과 입자 현상은 XRD와 SEM으로 특성을 관찰하였다. 조합검색 결과로부터 $Y_{1-x}(P_{1-y-z}Nb_yV_z)O_4:Eu_x$ 형광체의 발광특성은 P 자리에 치환되는 금속이온의 영향을 많이 받았다. 결과적으로 $Y_{0.88}PO_4:Eu_{0.12}$ 형광체와 비교하여 발광 효율이 우수한 새로운 $Y_{0.88}(P_{0.92}Nb_{0.05}V_{0.03})O_4:Eu_{0.12}$ 형광체를 찾아내었다.

• 센서학회지
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• 제10권6호
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• pp.295-303
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• 2001

형광체로서 ZnS를 사용하고 BST 강유전체 박막을 절연체로 사용한 전계발광소자를 제작하고 그 특성을 조사하였다. 형광체로는 청색 및 녹색발광을 위해 각각 $ZnS:AgF_3$와 ZnS:$TbF_3$를 사용하였으며 적색을 위해 ZnS:Mn과 $ZnS:SmF_3$를 사용했다. 이들의 형광체가 증착 도중에 분해되는 것을 막기 위해 석영관에 그들을 각각 봉입해서 열처리하여 결정화시킨 후에 진공증착원으로 사용하였다. 한편 절연층으로 사용한 BST박막은 $Ba_{0.5}Sr_{0.5}TiO_3$세라믹스 타겟을 사용하여 마그네트론 스퍼터링 방법으로 제조하였다. 이때 기판온도, 분위기압 및 작동기체인 $Ar:O_2$의 비가 각각 $400^{\circ}C$, 30 mTorr 및 9:1이였다. 각 형광체의 두께는 150 nm씩 합계 600 nm였고, 절연층은 상부가 400 nm 및 하두가 200 nm이었다. 이와 같이 만든 박막 전계발광소자의 발광 문턱전압은 $75\;V_{rms}$이고, 최고 휘도는 $100\;V_{rms}$에서 $3200\;cd/m^2$이었다. 그리고 절연층의 유전상수는 1 kHz에서 254이다.

• 한국표면공학회지
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• 제53권4호
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• pp.131-137
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• 2020

A series of Dy³⁺, Sm³⁺, and Dy³⁺/Sm³⁺ doped Gd₂WO₆ phosphors were synthesized by the conventional solid-state reaction. The X-ray diffraction patterns revealed that all of the diffraction peaks could be attributed to the monoclinic Gd₂WO₆ crystal structure, irrespective of the type and the concentration of activator ions. The photoluminescence (PL) excitation spectra of Dy³⁺-doped Gd₂WO₆ phosphors contained an intense charge transfer band centered at 302 nm in the range of 240-340 nm and two weak peaks at 351 and 386 nm. Under an excitation wavelength of 302 nm, the PL emission spectra consisted of two strong blue and yellow bands centered at 482 nm and 577 nm. The PL emission spectra of the Sm³⁺-doped Gd₂WO₆ phosphors had a series of three peaks centered at 568 nm, 613 nm, and 649 nm, corresponding to the ⁶G_5/2 → ⁶H_5/2, ⁶G_5/2 → ⁶H_9/2, and ⁶G_5/2 → ⁶H_11/2 transitions of Sm³⁺, respectively. The PL emission spectra of the Dy³⁺- and Sm³⁺-codoped Gd₂WO₆ phosphors showed the blue and yellow emission lines originating from the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁴H_13/2 transitions of Dy³⁺ and reddish-orange and red emission bands due to the ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 transitions of Sm³⁺. As the concentration of Sm³⁺ increased from 1 to 15 mol%, the intensities of two PL spectra emitted by the Dy³⁺ ions gradually decreased, while those of the three emission bands due to the Sm³⁺ ions slowly increased, thus producing the color change from white to orange. The CIE color coordinates of Gd₂WO₆:5 mol% Dy³⁺, 1 mol% Sm³⁺ phosphors were (0.406, 0.407), which was located in the warm white light region.

• 한국재료학회지
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• 제24권12호
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• pp.658-662
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• 2014

$Eu^{2+}/Dy^{3+}$-doped $Sr_2MgSi_2O_7$ powders were synthesized using a solid-state reaction method with flux ($NH_4Cl$). The broad photoluminescence (PL) excitation spectra of $Sr_2MgSi_2O_7:Eu^{2+}$ were assigned to the $4f^7-4f^65d$ transition of the $Eu^{2+}$ ions, showing strong intensities in the range of 375 to 425 nm. A single emission band was observed at 470 nm, which was the result of two overlapping subbands at 468 and 507 nm owing to Eu(I) and Eu(II) sites. The strongest emission intensity of $Sr_2MgSi_2O_7:Eu^{2+}$ was obtained at the Eu concentration of 3 mol%. This concentration quenching mechanism was attributable to dipole-dipole interaction. The $Ba^{2+}$ substitution for $Sr^{2+}$ caused a blue-shift of the emission band; this behavior was discussed by considering the differences in ionic size and covalence between $Ba^{2+}$ and $Sr^{2+}$. The effects of the Eu/Dy ratios on the phosphorescence of $Sr_2MgSi_2O_7:Eu^{2+}/Dy^{3+}$ were investigated by measuring the decay time; the longest afterglow was obtained for $0.01Eu^{2+}/0.03Dy^{3+}$.

• Current Optics and Photonics
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• 제3권6호
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• pp.590-596
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• 2019

To improve the color gamut of a liquid-crystal display (LCD), we propose a bandpass filter that is added to the backlight unit to optimize the backlight spectrum. The bandpass filter can only transmit red, green and blue light in the visible range, while reflecting the unwanted light. We study the optical properties of the bandpass filter using the transfer-matrix method, and the effect of the bandpass filter on the color gamuts of LCDs is also investigated. When a bandpass filter based on a 5-layer configuration comprising low and high refractive indices ((HL)²H) is used in phosphor-converted white-light-emitting diode (pc-WLED), K₂SiF₆:Mn⁴⁺ (KSF-LED), and quantum-dot (QD) backlights, the color gamuts of the LCDs improve from 72% to 95.3% of NTSC, from 92% to 106.7% of NTSC, and from 104.3% to 112.2% of NTSC respectively. When the incident angle of light increases to 30°, the color gamuts of LCDs with pc-WLED and KSF-LED backlights decrease by 2.9% and 1% respectively. For the QD backlight, the color gamut almost does not change. When the (HL)²H structure is coated on the diffusion film, the color gamut can be improved to 92.6% of NTSC (pc-WLED), 105.6% of NTSC (KSF-LED), and 111.9% of NTSC (QD). The diffusion film has no obvious effect on the color gamut. The results have an important potential application in wide-color-gamut LCDs.

• Journal of Advanced Marine Engineering and Technology
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• 제39권4호
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• pp.473-477
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• 2015

본 논문에서는 인광물질을 포함하는 조명용 백색 LED를 이용한 가시광 통신 시스템의 변조 대역폭을 늘리기 위한 등화기를 설계하고 실험적으로 결과를 보였다. 등화기의 성능을 분석하기 위한 해석적 방법으로 회로 시뮬레이터인 PSpice를 이용하였다. 등화기는 저항과 커패시터를 이용한 수동필터와 증폭기를 이용한 능동필터의 조합으로 구성하였다. 등화기를 수신단에 적용함으로써 3.5 MHz 부근의 인광성 백색 LED 변조 대역폭이 청색 광학필터를 사용하지 않고도 25 MHz 까지 확장되었다. 상용화된 라운드형 백색 LED 1개와 PIN형 광 다이오드 1개를 이용하여 구현한 가시광 통신 시스템에서 진폭편이변조 방식으로 변조된 LED의 가시광 신호는 1미터 거리에서 35 Mbit/s 데이터 전송률을 보였다. 이때의 비트 에러율은 $7.6{\times}10^{-4}$이었으며 이는 순방향 오류 정정의 한계인 $3.8{\times}10^{-3}$ 이하를 만족하였다.

• 조명전기설비학회논문지
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• 제13권1호
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• pp.9-14
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• 1999

삼파장 형광등의 제작에서 문제가 되는 것은 원하는 목표 색을 맞추기 위하여 혼합하는 세 가지 형광물질의 혼합비율이다. 한 형광체의 광 스펙트럼이 약간 변형되거나, 공정변수에 의하여 변경되거나, Ar과 Kr 같은 불활성가스의 스펙트럼이 혼재하거나 또는 재래 할로인산칼슘이 공존할 경우 원하는 정확한 색을 찾기가 매우 힘들어지게 된다. 이 연구에서는 원하는 목표 색을 빠르게 찾는 방법을 연구하였다. 세 개의 각각의 단일색의 형광등과 3색을 서로 다른 비율로 혼합한 형광등을 만들고 각각의 스펙트럼을 측정한 후 이로부터 알곤과 수은의 스펙트럼을 빼서 변형 색 좌표를 얻었다. 이 변형 색 좌표로부터 적생에 대한 청색과 녹색의 광속비를 그의 무게 비에 대하여 도시하여 무게 대 광속비의 관계를 구하였다. 이 관계식을 이용하여 생산라인에서 삼파장 형광체의 단일 도포 및 할로인산칼슘을 1차로 도포하는 2중 도포를 실시하여 목표색을 조합해본 결과 만족할만한 결과를 얻었다.

• 한국재료학회지
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• 제21권12호
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• pp.644-649
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• 2011

[ $A_{3-2x/3}Al_{1-z}In_{z}O_4F:Eu_x^{3+}$ ](A = Ca, Sr, Ba, x = -0.15, z = 0, 0.1) oxyfluoride phosphors were simply prepared by the solid-state method at $1050^{\circ}C$ in air. The phosphors had the bright red photoluminescence (PL) spectra of an $A_{3-2x/3}Al_{1-z}In_{z}O_4F$ for $Eu^{3+}$ activator. X-ray diffraction (XRD) patterns of the obtained red phosphors were exhibited for indexing peak positions and calculating unit-cell parameters. Dynamic excitation and emission spectra of $Eu^{3+}$ activated red oxyfluoride phosphors were clearly monitored. Red and blue shifts gradually occurred in the emission spectra of $Eu^{3+}$ activated $A_3AlO_4F$ oxyfluoride phosphors when $Sr^{2+}$ by $Ca^{2+}$ and $Ba^{2+}$ ions were substituted, respectively. The concentration quenching as a function of $Eu^{3+}$ contents in $A_{3-2x/3}AlO_4F:Eu^{3+}$ (A = Ca, Sr, Ba) was measured. The interesting behaviors of defect-induced $A_{3-2x/3}Al_{1-z}In_{z}O_{4-{\alpha}}F_{1-{\delta}}$ phosphors with $Eu^{3+}$ activator are discussed based on PL spectra and CIE coordinates. Substituting $In^{3+}$ into the $Al^{3+}$ position in the $A_{3-2x/3}AlO_4F:Eu^{3+}$ oxyfluorides resulted in the relative intensity of the red emitted phosphors noticeably increasing by seven times.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

• E2M - 전기 전자와 첨단 소재
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• 제12권7호
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• pp.7-11
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• 1999

Fully sealed field emission display in size of 4.5 inch has been fabricated using single-wall carbon nanotubes-organic vehicle com-posite. The fabricated display were fully scalable at low temperature below 415$^{\circ}C$ and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1V/${\mu}{\textrm}{m}$ and field emis-sion current of 1.5mA at 3V/${\mu}{\textrm}{m}$ (J=90${\mu}{\textrm}{m}$/$\textrm{cm}^2$)were observed. Brightness of 1800cd/$m^2$ at 3.7V/${\mu}{\textrm}{m}$ was observed on the entire area of 4.5-inch panel from the green phosphor-ITO glass. The fluctuation of the current was found to be about 7% over a 4.5-inch cath-ode area. This reliable result enables us to produce large area full-color flat panel dis-play in the near future. Carbon nanotubes (CNTs) have attracted much attention because of their unique elec-trical properties and their potential applica-tions [1, 2]. Large aspect ratio of CNTs together with high chemical stability. ther-mal conductivity, and high mechanical strength are advantageous for applications to the field emitter [3]. Several results have been reported on the field emissions from multi-walled nanotubes (MWNTs) and single-walled nanotubes (SWNTs) grown from arc discharge [4, 5]. De Heer et al. have reported the field emission from nan-otubes aligned by the suspension-filtering method. This approach is too difficult to be fully adopted in integration process. Recently, there have been efforts to make applications to field emission devices using nanotubes. Saito et al. demonstrated a car-bon nanotube-based lamp, which was oper-ated at high voltage (10KV) [8]. Aproto-type diode structure was tested by the size of 100mm $\times$ 10mm in vacuum chamber [9]. the difficulties arise from the arrangement of vertically aligned nanotubes after the growth. Recently vertically aligned carbon nanotubes have been synthesized using plasma-enhanced chemical vapor deposition(CVD) [6, 7]. Yet, control of a large area synthesis is still not easily accessible with such approaches. Here we report integra-tion processes of fully sealed 4.5-inch CNT-field emission displays (FEDs). Low turn-on voltage with high brightness, and stabili-ty clearly demonstrate the potential applica-bility of carbon nanotubes to full color dis-plays in near future. For flat panel display in a large area, car-bon nanotubes-based field emitters were fabricated by using nanotubes-organic vehi-cles. The purified SWNTs, which were syn-thesized by dc arc discharge, were dispersed in iso propyl alcohol, and then mixed with on organic binder. The paste of well-dis-persed carbon nanotubes was squeezed onto the metal-patterned sodalime glass throuhg the metal mesh of 20${\mu}{\textrm}{m}$ in size and subse-quently heat-treated in order to remove the organic binder. The insulating spacers in thickness of 200${\mu}{\textrm}{m}$ are inserted between the lower and upper glasses. The Y\ulcornerO\ulcornerS:Eu, ZnS:Cu, Al, and ZnS:Ag, Cl, phosphors are electrically deposited on the upper glass for red, green, and blue colors, respectively. The typical sizes of each phosphor are 2~3 micron. The assembled structure was sealed in an atmosphere of highly purified Ar gas by means of a glass frit. The display plate was evacuated down to the pressure level of 1$\times$10\ulcorner Torr. Three non-evaporable getters of Ti-Zr-V-Fe were activated during the final heat-exhausting procedure. Finally, the active area of 4.5-inch panel with fully sealed carbon nanotubes was pro-duced. Emission currents were character-ized by the DC-mode and pulse-modulating mode at the voltage up to 800 volts. The brightness of field emission was measured by the Luminance calorimeter (BM-7, Topcon).